Int 68 Fn 03  - Appc/pc - Change Logical Unit                              [N]

   AH = 03h subfn 2A00h
   DS:DX -> control block (see below)

Return: control block updated

Format of control block:
Offset Size    Description
 00h 12 BYTEs  reserved
 0Ch   WORD    2A00h (verb "Change Logical Unit")
 0Eh  6 BYTEs  00h
 14h   DWORD   (big-endian) return code (see AH=01h/SF=1B00h)
 18h   WORD    00h
 1Ah  8 BYTEs  (big-endian) logical unit ID
 22h   DWORD   pointer to CREATE_TP_EXIT routine
       FFFFFFFFh reject incoming ALLOCATEs
       00000000h queue ALLOCATEs
 26h   DWORD   00000000h
 2Ah   DWORD   pointer to SYSTEM_LOG_EXIT routine, FFFFFFFFh= don't log errors
 2Eh   DWORD   00000000h
 32h   BYTE    maximum TPs
 33h   BYTE    00h stop QUEUE_ALLOCATEs
       01h resume QUEUE_ALLOCATEs
 34h   DWORD   pointer to LU_LU_PASSWORD_EXIT routine, FFFFFFFFh = no exit
 38h   DWORD   00000000h